Recently, various LCD products have become popular for use in mobile hand-held devices. In addition, due to widespread use of smart end devices, integration of a touch function into smart end devices has become a mainstream demand for current products.
Referring to FIG. 1, a conventional touch display apparatus having a touch display function initiates a touch driver in a display-pause period for touch driving. As shown, FIG. 1 is a waveform schematic diagram of a conventional shift register having a touch display function, where a display panel has a plurality of scan lines, and a scan driver comprising multi-stage shift register circuits, a clock signal CK, scan signals G(n−1), G(n), and driving voltages Q(n−1), Q(n). In each frame period, the shift register circuits output the scan signals according to the clock signal to enable the corresponding scan lines of the display panel. For example, the shift register circuits may raise the driving voltage Q(n−1) of an internal driving node Q according to the clock signal CK to output the scan signal G(n−1). In a display-pause period, the shift register circuits are disabled and suspended from outputting the display scan signal G(n), and all of the external signals such as the clock signal CK are disabled therefore the driving voltage Q(n) of the driving node Q is in a floating state at this time, resulting in leakage of the driving voltage Q(n) of the driving node Q with time. The longer the external signals such as the clock signal CK are disabled, the more leakage of the driving voltage Q(n) will occur. When the display driving is restored, the scan signal G(n−1) has leakage due to the floating of the internal driving node of the display driving circuit in the display-pause period, causing failure of the scan signal G(n) after the display-pause period to output a correct voltage level, thereby degrading the display quality. In addition, the waveform distortion of the restored scan signal G(n) results in inconsistency between the time of a falling edge in the waveform and the time of a falling edge of scan signals from other stages, causing the mura effect. Moreover, the display-pause period generally occurs at a constant time frame for the scan lines. Since the driving nodes Q of the previous-stage and next-stage shift register circuits are also in the leakage state due to floating, a gate end of a driving transistor of the driving unit for pulling down the scan signals G(n−1), G(n) is continuously stressed, such that the threshold voltage of the driving transistor drifts.
Thus, how to prevent the driving transistor of the shift register circuits from being stressed for a long time, resulting in component performance deterioration and thus erroneous output is one of the important development issues today, and also has become an object urgently in need of improvement in related fields today.